Ectopic expression of Dl and Ser A. Outline of expression plasmids, incorporating β-globin leader sequences, SV40 poly A. An XbaI site at the cytoplasmic face of the transmembrane domain (X, shaded) allowed us to construct chimeric transgenes expressing the intracellular domain of one protein and extracellular and transmembrane domain of the other, as well as Dl and Ser transgenes with and without the XbaI site B-D. Cut protein induction at the developing dorso-ventral margin of wing imaginal discs dissected from white prepupae. B. wildtype. C. In dppGal4>SEDI ectopic wing margin is induced ventrally, as described previously for Ser. D. In dppGal4>DESI ectopic wing margin is induced dorsally, as described previously for Dl. E-G. Nuclear Elav protein in photoreceptor cells differentiating in the posterior eye imaginal disc. E. Wild type clusters contain 8 differentiating cells. F. In scaGal4>SESI the number of differentiating cells is reduced, as described previously for Ser. G. In scaGal4>DEDI the number of photoreceptors per cluster is also reduced.